There are air blower units provided in outdoor units of air conditioners, in which, for example, fan guards are provided at air outlets of blower fans for protecting the blower fans.
As the above fan guards, there are well known fan guards in which many radially arranged radial ribs and many coaxially arrange annular ribs are formed integrally by a synthetic resin. The radial ribs and the annular ribs of such fan guards made of a synthetic resin have flat sections along the direction of the rotation axis of the blower fans for maintaining the strength and reducing pressure loss of forced airflow flowing between the ribs.
As a function that the fan guards with such a structure are required to have, the fan guards should have enough strength to prevent fingers or foreign matters from entering in error between the annular ribs.
Pushing an object of a given size with a given force expands the intervals of the annular ribs, so that the object enters. As the strength of the fan guards with the above structure to prevent this entering, strength at the outermost peripheral part where the intervals of the radial ribs become the widest is used as a reference value for design.
However, the intervals of the radial ribs of the fan guards of this type are narrower as it approaches the center, which invites increase in ventilating resistance and in noise. In order to tackle these disadvantages, a fan guard has been proposed which restrains excessive increase in the ventilating resistance in the interior part by thinning the radial ribs inside a point where the intervals of the radial ribs are smaller as it goes inward and the rib density is twice as high as a reference, which means intervals of the radial ribs at the outermost periphery (for example, Japanese Patent Application Laid Open Publication No. 2002-195610).
Problems to be Solved
Referring to fan guards of air blower units used in apparatuses provided outdoors, such as outdoor units for air conditioners, it includes providing a function of preventing breakage of the blower fan, which results from contact with the rear edge of a vane of the blower fan due to bending of the fan guard, in addition to the function of preventing foreign matter from entering between the annular ribs. The causes of the fan guard bending include: an object such as a ball collides with the fan guard, to bend the central part of the fan guard; snow in winter accumulates on the fan guard where the rotary shaft of the blower fan is arranged perpendicularly upward, so that the weight of the snow bends the fan guard.
The fan guards with the above structure are fixed at outer frames thereof to the unit bodies. Therefore, the radial ribs works more than the annular ribs for preventing deformation due to load application to the central parts of the fan guards. Hence, the number, the arrangement, the shape of the section and the like of the radial ribs influence much the strength against bending.
However, in the case where the inner radial ribs are thinned in the fan guard as disclosed above, the increase in the ventilating resistance is suppressed while the strength against bending at the central part decreases, with a result that the fan guard is liable to be deformed due to load application to the central part. Thus, the vanes of the blower fan may come into contact with the thus deformed part of the fan guard.
The present invention has been made in view of the above problems and features preventing the increase in the ventilating resistance of the forced airflow while ensuring strength to prevent rib expansion and the strength to prevent bending of the fan guard.